Visible GOES-17 satellite image of Potential Tropical Cyclone Nine at 15:20Z (11:20 a.m. EDT) Wednesday, July 29, 2020. (Image credit: NOAA/RAMMB)

A large and vigorous tropical wave in the eastern Caribbean, designated Potential Tropical Cyclone Nine (PTC 9) by NOAA’s National Hurricane Center, was spreading heavy rain showers on Wednesday over much of the Leeward Islands, Virgin Islands, Puerto Rico, and the Dominican Republic, as seen on long-range radar out of Puerto Rico and Martinique.

Rainfall amounts in the islands as of 11 a.m. EDT Wednesday were mostly less than an inch, though a personal weather station on Dominica received 3.13″ in 24 hours.

As of that time, PTC 9 had top sustained winds near 45 mph and a central pressure of 1006 mb, and was headed west-northwest at 23 mph. PTC 9 is predicted to bring tropical storm conditions with heavy rains of 3 – 6 inches to the Leeward Islands, the Virgin Islands, Puerto Rico, Dominican Republic, northern Haiti, and Turks and Caicos Islands over the next few days. Higher rainfall amounts of 4 – 8 inches were predicted for the Inagua Islands.

Figure 1. A heavy rain shower from PTC 9 moving in over St. Barts in the Leeward Islands at 9:09 a.m. local time July 29, 2020. Thanks go to Caribboy for this link. (Image credit: webcam)

An Air Force hurricane hunter aircraft investigating the storm Wednesday morning was unable to find a well-defined surface circulation, so PTC 9 retained its ungainly moniker. Satellite images on Wednesday showed that PTC 9 was steadily growing more organized, with more low-level spiral bands and an area of intense thunderstorms consolidating near what appeared to be a developing surface circulation center. The storm is also expected to slow down in forward speed through Thursday, favoring development and making it likely that PTC 9 will be named “Isaias” (pronounced ees-ah-EE-ahs) by Wednesday night. If so, that would beat the record for earliest ninth storm in Atlantic tropical cyclone history set by Irene on August 7, 2005.

PTC 9 had favorable conditions for development on Wednesday afternoon, with sea surface temperatures (SSTs) near 29 degrees Celsius (84°F) and light wind shear of 5 – 10 knots. The system was embedded in a moderately dry atmosphere with a mid-level relative humidity of 55%, but the light wind shear to a large extent was allowing the storm to wall off the dry air of the Saharan Air Layer to its north.

Figure 2. Predicted surface wind (colors) and pressure (black lines) at 6Z (2 a.m. EDT) Friday, July 31, 2020, from the 6Z Wednesday, July 29, 2020 run of the HWRF model. The model predicted that PTC 9 would be approaching the Bahamas as a disorganized tropical storm with peak winds of 48 knots (55 mph, yellow colors) and a central pressure of 999 mb. (Image credit: Tropical Tidbits)

Forecast for PTC 9

The prospects that PTC 9 eventually will attain hurricane strength look dimmer than they did on Tuesday, but the uncertainty in the future of the storm remains very high until it forms a well-defined center and gets named.

As PTC 9 moves west-northwestward, it will have to contend with passage over Hispaniola on Thursday, and the mountainous terrain on the island could significantly disrupt PTC 9’s circulation. Passage close to the mountainous terrain of eastern Cuba on Friday may also act to disrupt the storm. In addition, PTC 9 will also have to contend with dry air from the Saharan Air Layer, located to the north. The 12Z Wednesday run of the SHIPS model predicted that the atmosphere surrounding PTC 9 would slowly dry to a relative humidity of 45% by Thursday evening. The model also predicted that wind shear would rise to a moderately high 15 – 25 knots on Thursday through Saturday, which should retard development.

However, SSTs for PTC 9 will warm to 30 degrees Celsius (86°F) by Saturday, which will aid the intensification process. Also favoring intensification will be a large-scale region of ascending air over the Atlantic, caused by passage of an atmospheric disturbance called a Convectively Coupled Kelvin Wave.

The 11 a.m. EDT Wednesday National Hurricane Center (NHC) intensity forecast called for PTC 9 to remain below hurricane strength, peaking with 60 mph winds this weekend. Nearly all of the top intensity models also predicted that PTC 9 would not become a hurricane.

The three best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – all support intensification of PTC 9 into a tropical storm by Thursday, July 30. In an 8 a.m. EDT Wednesday Tropical Weather Outlook, NHC gave PTC 9 two-day and five-day odds of formation of 90%.

PTC 9’s rains beneficial for drought-stricken Caribbean islands

Many of the Caribbean islands in the path of PTC 9 will welcome its heavy rains, since they will help alleviate moderate to severe drought conditions from an unusually dry spring and first half of summer.

Figure 3. Palmer Drought Severity Index (PDSI) for Puerto Rico and the U.S. Virgin Islands for July 23, 2020, showed much of the islands in moderate to severe drought. Regions marked with an “S” imply mostly short-term impacts to agriculture. (Image credit: U.S. Drought Monitor)

Climate change is likely partly to blame for the drought, as explained in a 2018 study, Exacerbation of the 2013–2016 Pan‐Caribbean Drought by Anthropogenic Warming. The authors of that research found that human‐caused warming contributed to 15 – 17% of the severity of the intense 2013 – 16 drought in the Caribbean, and 7% of its spatial extent. The findings “strongly suggest that climate model projected anthropogenic drying in the Caribbean is already underway, with major implications for the more than 43 million people currently living in this region,” they concluded.

This year’s drought is particularly acute in Puerto Rico, where over half of the island was in drought on July 23, according to the U.S. Drought Monitor product. The governor declared a state of emergency in late June and ordered water rationing, subjecting residents in affected areas to 24-hour water shutoffs every other day. Loss of running water makes living through a pandemic deadlier, since residents are unable to wash hands, bathe, and disinfect surfaces as often as needed to avoid spread of the coronavirus.

How inequality grows in the aftermath of hurricanes

According to Princeton’s Latin American Flood and Drought Monitor, the Dominican Republic is experiencing the worst drought in the Caribbean. To illustrate, rainfall amounts between June 15 and July 27 at Barahona, on the southwest coast of the Dominican Republic, were just 0.09″ (2.2 mm). The capital, Santo Domingo, received 0.44″ (11.3 mm) during the same period. Haiti is also under severe drought, putting much of the nation into a food crisis, according to the Famine Early Warning Systems Network.

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Jeff Masters

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...

365 replies on “Rain from Potential Tropical Cyclone Nine brings drought relief to Caribbean islands”

  1. Afternoon all. I’m happy to see PTC9 is bringing the best of itself to the NE Car …. and congrats to Caribboy on the shout out in the article ….

    On the drought situation in Hispaniola, I have a sneaking suspicion their rain has been falling over the Bahamas for the last few weeks. It’s been considerably rainier than usual here this July.

    I’m still feeling hopeful that PTC 9 will remain largely a drought-buster throughout its lifetime, without causing serious damage.

      1. Hey Baha and Pottery. This is Castastrophe Adjuster. Don’t know if this is going to post or not can’t figure it out yet.

  2. 29/1730 UTC 16.1N 64.6W T2.5/2.5 09L — Atlantic

    AL, 09, 2020072918, , BEST, 0, 161N, 649W, 40, 1006, LO

    They all most agreed with one other

  3. Saludo, ahora en este momento en Humacao,PR no tenemos energía eléctrica mi estación del tiempo lee presión Barométrica 29.62(1003.1mb) viento 28mph ráfagas de 42mph lloviendo fuerte en bandas se escuchan tronadas fuertes al sureste de mi poscion.

  4. Hi guys! Just reposting from the Cat6 blog:

    Hello once again reporting from San Juan, PR

    We’re getting a second heavy rain / wind band. Have a really good video of that first band, but you know, Disqus upload limits. Have it on Facebook, just search Carlos Alberto Garcia Chandler and the handsome guy with the machete in hand after Hurricane Maria, that’s me.

    The first PTC9 band effectively knocked out power to most people – mind you, around 3 to 3.2 million people live in the Island.

    Currently operating on solar power / battery backup.

    Landline cable Internet still operating, I’m lucky. You guys lost me for months after María because I got power almost four months after, and all that time with little to no cellphone service, let alone Internet, and let alone broadband – all that came months to a year later.

    Reckon we haven’t gotten hit by the bread and butter of the storm yet. Haven’t done a proper weather analysis, just got off work.

    There is low voltage situation on power lines so all sensitive equipment must be disconnected / breakers off for things like inverter air conditioners. If you can throw off the main grid disconnect then that would be the proper way to go.

    1. Hope you get power back without delay ….
      I feel you on the power / internet… After Matthew we were off for more than 3 weeks and even now connectivity during thunderstorms is iffy ….
      Take care!

      1. Thanks. Thankfully once I moved to San Juan a year ago (and bought a home) one of the first mods was a solar & battery back up emergency power system. Sometimes I go weeks off grid just for kicks. But it needs 1kw more on panels to get it’s groove on better… right now, I can do 2.5 days with 100% blackout stormy skies if I ration things well enough. Can’t charge my batteries fast enough (1kw in panels for 5.4kwh in batteries).

  5. Hey, I’m unable to comment on the mobile version… and where do you sign up? I only see login which doesn’t give me the option to create an account.

    1. Just log in with your screen name, and e-mail address (IIRC, you’ll have to verify the e-mail address). You can leave the last line empty. You’ll be good to go.

      1. I did neither of those things and am able to comment easily. Message input box remembers my name and email so I don’t actually need to type anything (after the first time). I never had to “log in” and never had to verify any email address.

    1. You’re absolutely right, Beell! Determining when and where it begins to move poleward, will ultimately dictate whether or not FL sees a landfalling system. The race against that short-wave propagating southward is on.

      If I may ask, what’s your best guesstimate at this time? Into the peninsula, a side swipe/coastal scrapper, or well east thereof?

      Thanks in advance, =)

  6. The drought situation seems untenable. I hope this alleviates it for the region, but not overwhelming them with floods – of dried and hardened soil creating fast run-off. Another hope is Venezuela gets some of those healthy rain bands. Their situation seems dire. From The Borgen Project:

    • Almost 80% of VZ’s electricity comes from hydroelectric. They’ve been experiencing a three-year drought. Shortening the work week, accelerating their economic collapse.
    • Petroleum products made up 93% of their $63 billion in exports for 2014. No doubt worsened with the collapse of the market. Their inflation rate is an astonishing 10,398% over the past three years.
    • Food and water shortages are at an all-time high. Since 2017, two-thirds of VZ residents have lost an average of 25 pounds in the previous year.
    • Up to 87% of the population cannot afford essential food. A staggering 72% of monthly wages are spent on food alone.
    1. Also, PR’s “drought” is in part just plain old mismanagement. PR’s water works company (state owned, the only one on the Island) loses almost 60% of the water it produces in broken pipes, stolen water, and other ways.

      Also, our reservoirs are severely sedimented – an example is Carraízo (gives water to at least half of the Metro area): it’s been over 20 years since it was dredged, and current estimates is that it’s lost at least 60% of it’s capacity.

      1. Yes, thanks for that direct info. No doubt very similar to here in Saipan, though we have a much smaller scale of population. Some estimates of 50-60%+ water loss due to theft, leaky pipes, poor/aged infrastructure. But here also lack of expertise. In Saipan we have basically no freshwater lakes or rivers. And wells are causing all sorts of problems. Our tap water isn’t even close to drinkable.

        But all in all, I know it’s nothing compared to the challenges Puerto Rico faces. In hope PREPA gets sorted out, your drought alleviated, and please stay safe. Best thoughts with my fellow islanders!

  7. Thank You Dr. Masters. I’m glad to see that PTC 9 has many obstacles in its path and slimmer chances of becoming a hurricane.

  8. Hi! Still getting used to commenting on here… it’s already improved a lot since they first rolled it out yesterday. The 12z Euro is certainly very interesting. It looks like we might see a center try to form in the central/northern part of PTC9, which could actually close off due to land friction as it’s passing Puerto Rico/Hispaniola. This is similar to the scenario shown on some of the EPS ensembles from earlier today, as well as the HWRF and HMON models. We could definitely see a more intense system near the Bahamas if this verifies, though given unfavorable environmental conditions I doubt it would be more than a minimal hurricane at the very most.

    1. Try over the Bahamas… on approach to FL… not near ’em. Nevertheless, I digress, =)

  9. Thanks for the new blog entry, Doc! Nice to hear that PTC09 will likely be a beneficial rain event for many islands. Hope for them it pans out that way!
    Unfortunately there is no tropical storm under way to central Germany which could use a fat drenching as well.

    1. Please, no. We bugged out to Sarasota last year. I have no desire to go into the belly of the COVID-19 beast this year.

    1. I don’t think you do. I was asking the same thing yesterday. Put in your email and user name when you post or reply. It just goes through. I’m posting and I never “signed up” or “registered” in any way.

  10. Reminds me of micheal with all the models having a hard time with intensity going even a few days after

  11. Maria, 7.6 earthquake, money to rebuild homes not allocated to the people, now a drought. Puerto Rico just had a massive power grid failure affecting 400,000 people yesterday. As of Tuesday night they had not found the source of the problem.

    1. Hey, some of the residents got a roll of paper towels thrown to them after Maria. What else could they possibly want or need after that?

      1. A year later the world would find out Maria really killed closer to 5,000 people, then the earthquakes came; meanwhile most homes never got repaired from the funds meant to do so. Can’t imagine 400K being without power now as the next storm bares down, no AC, hadn’t found the issue last I checked. Dew Point 77/92 heat index currently in San Juan.

    2. Brother, I feel for all you fellow islanders (I’m in Saipan). I cannot understand how PREPA is handling things, privatizing; basically looting the population for the benefit of ogligarch mainlanders. Disgusting. I’d personally listened to Cobra Energy (one of the big PR energy restoration contractors after Maria) pitch to CNMI figureheads how they could help – yeah, find their next cash cow, is about all). Wishing you all the best from the other side of the world, as another vulnerable U.S. territory. Stay safe.

      This from HuffPost and reprinted by Grist without paywall:

      1. We’re sure thinking of you all, very sorry so many are suffering so. Most of us here have never forgotten what happened, and continues to happen to Puerto Rico and the Islands. It’s wrong and the corruption blatent.

      2. Wait, I thought you are in Puerto Rico? No? Sorry if I am confused, misunderstood, misremembered…

      3. South Carolina here, but I keep up with what’s going in Puerto Rico daily. All the best! Saipan’s an amazing place with an amazing history. Super Typhoon Yutu was terrifying, and I know you all know Puerto Rico’s plight unfortunately well.

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